What would you write in a bereavement/sympathy card?

My grandmother (Dad’s Mum) died last night and as I am in the UK and my parents and family are in Australia, I am going to send my parents a sympathy card. On the front it says ‘Deepest Sympathy’ and inside it says ‘Thinking of you at this time’.

I really can’t think of anything else to write in it except to address it to Dad and Mum and to sign off ‘with love’. Do I need to write anything else?
I am not really close to my father and he didn’t have a very good relationship with his mum, so I don’t want to be too wordy or emotional, we’re not like that as a family.
I actually will be there with them on th e1st September, which is why it’s such a blow that she died a week and a half before I got there. I was thinking of saying looking forward to seeing you soon, but that sounds selfish and frivoulous. Maybe I could say wish I could be there, as you suggest.
Both my parents are atheists but I appreciate your comments.